Multi-bit reconfigurable resonator using tapped transmission line and RF switches

Most of current mobile communication terminals are installed with multiple radio circuits and choose one of them to operate in an assigned frequency band. In order to make more efficient use of frequency spectrum and to reduce RF circuits of the future mobile terminals, reconfigurable RF circuits will be necessary that can adapt to many frequency bands. This paper proposes a new multi-bit reconfigurable resonator that can change its resonant frequency among 2^N values with N RF switches and a tapped transmission line. As the simplest case, two-bit reconfigurable resonators employing λ/2 resonant mode and λ/4 resonant mode are examined in detail. Their frequency characteristics are analyzed including the loss of the RF MEMS switches by circuit simulation. A preliminary prototype using a micro strip line on a high dielectric substrate has been fabricated and evaluated for a two-bit λ/4 mode resonator. The resonators can be cascaded to form a reconfigurable low-loss bandpass filter.